I have tended to add options to Page (so everypage) but with a set of defaults so 90% of the time they dont need to change the options. And if this is on Page they can override options on a page by page option. But for site wide settings doing it on the homepage is probably the next most easiest thing

Not currently sadly, only way would just to to make a SiteConfig page type with all the fields etc, and extend it off a redirector page? rather then a page. So it would still be a page in the site tree and have a url like /site-config/ but if a user hit it on the front end it would redirect them to the homepage or something. You could also hide it from search and menus so Its 'Invisible' in a sense